MQTT modules are devices for communication and data exchange in IoT and M2M systems. They use the lightweight and efficient MQTT protocol for message transmission. These modules allow publishing and subscribing to different topics, enabling efficient and distributed communication. They are often integrated into sensors, controllers or IoT gateways and provide reliable communication between devices and the central system. MQTT modules are a popular solution for communication in IoT and M2M environments due to their simplicity, efficiency and broad support in industrial sectors.